a) Field of the Invention
The invention relates to an adjustable steering column for a motor vehicle, and includes a setting unit displaceable in at least one setting direction, a holding unit nondisplaceable in this setting direction and a securement device. In the opened state of the securement device, the setting unit is displaceable with respect to the holding unit for setting the position of the steering column, and in the closed state of the securement device, the setting unit is secured in place by the securement device. The securement device comprises a clamp bolt, penetrating openings in the setting unit and the holding unit, at least one tooth plate penetrated by the clamp bolt, which tooth plate comprises at least one toothing with teeth directed away from the clamp bolt, and at least one toothing, facing the clamp bolt, of the holding unit for cooperation with the at least one toothing of the tooth plate in the closed state of the securement device.
b) Description of Related Prior Art
Adjustable steering columns serve for the adaptation of the position of the steering wheel to the seating position of the driver and are known in diverse embodiments. Apart from adjustable steering columns which are only adjustable with respect to the directions of length or height or inclination, steering columns are also known which are length—as well as also height—or inclination-direction adjustable. Such an adjustable steering column is disclosed, for example, in EP 0 802 104 A1. In the opened state of the securement device, a setting unit rotatably bearing-supporting the steering spindle is displaceable with respect to a chassis-stationary holding unit in the direction of a length adjustment as well as also in the direction of a height or inclination adjustment of the steering column. To increase the holding forces in the closed state of the securement device, the securement device comprises intersecting disk packs cooperating in the manner of a multi-disk coupling.
For adjustable steering columns the problem is encountered that in the event of a crash, uncontrolled displacement of the steering column must be prevented such that, for example, the function of the airbag is not impaired and/or the energy upon the impact of the driver onto the steering wheel can be dissipated under control. The securement device should at the same time be readily-moved and it should be possible to open and close the device with minimal strokes of the actuation members and it should assume only low installation space.
In addition to adjustable steering columns with securement devices acting under frictional locking, securement devices are known which act under positive locking, in which in the closed state toothed securement elements come into engagement with one another. One problem entailed therein is that during the closing the teeth of the securement device can impact one another directly. Several devices intended to prevent this have become known. EP 1 500 570 A2 discloses securement elements utilized herein, which have rows of toothings offset with respect to one another. The toothings are here disposed on faces of tooth bars positioned in the form of wedges with respect to one another, in which bars are held in a base body penetrated by the clamp bolt of the securement device.
U.S. Pat. No. 6,139,057 A discloses a positive locking securement device in which, through the closing of the securement device, tooth parts swivellable through an actuation lever come to mesh with countertoothings. If during the closing of the securement device the tips of the teeth of the toothing of a tooth part impact the tips of the teeth of the countertoothing (this position is also referred to as “tooth-on-tooth position”), to make possible the complete swivelling of the actuation lever into its closure position without too great a resistance, the plates of sheet metal bearing the toothings are elastically supported with respect to the shaft bearing them. In order to obtain tooth meshing in all setting positions of the setting unit, for each setting direction two adjacent tooth plates with offset teeth are provided.
Further, US 2006/0090586 A1 discloses an adjustable steering column of the above described type in which, in the closed state of the securement device, for the friction-locked retention system of the setting unit with respect to the holding unit, side jaws of the chassis-stationary holding unit are pressed onto the setting unit. In order to prevent in the event of a crash an uprighting or pop-up (=an inclination or height adjustment) of the steering column, a toothed plate disposed rotatably on the clamp bolt with a toothing implemented on a side edge is additionally provided. When closing the clamping lever, the toothing of the tooth plate is pressed against a countertoothing by a spring entrained by the clamping lever. During the opening of the clamping lever, the tooth plate is swivelled through an actuator of the clamping lever about the axis of the clamp bolt and brought out of engagement with the countertoothing. In the event of a crash, the toothing, if it has not already been brought into engagement with the countertoothing during the closing of the securement device, after a small initial shift of the setting unit and a dislocation of the clamp bolt concomitant therewith and the tooth plate disposed thereon, is brought into engagement with the countertoothing. Since in the closed state of the securement device the tooth plate is only pressed against the countertoothing by the spring, in the event of a crash there can be the risk of the two toothings slipping through, and accordingly, the spring must be designed such that it is very strong. Thereby, the closing force for the securement device is increased.
DE 10 2004 051 060 B3 shows an adjustable steering column in which a crash blocking device is provided, from which, in the event of a crash, an additional holding force is exerted against a dislocation of the setting unit with respect to the holding unit. In the event of a crash, a clamping wedge is pushed into a gap between the setting unit and the holding unit. The clamping wedge is connected with a part of the securement device which moves during the opening and closing of the securement device, such that during the closing of the securement device, a contact face of the clamping wedge can be placed onto a locating face of the setting unit, in order to entrain by it the clamping wedge in the event of a crash at an onsetting dislocation of the setting unit.